The cariogenic properties of Streptococcus mutans will be analyzed utilizing genetic techniques. Initially, a partial genetic map of the S. mutans GS5 chromosome will be constructed following transformation of the organism with DNA containing a variety of genetic markers (amino acid auxotrophs, antibiotic resistance, amino acid analogue resistance). Linkage analysis will be conducted to localize genes coding for proteins postulated as cariogenic factors. In this regard, mutants of strain GS5 defective in glucosyltransferase and dextranase activities, agglutination, and bacteriocin production will be isolated in order to map the relative position of each of these genes. The strain GS5 gene coding for dextranase activity will also be isolated following cloning into the Streptococcus sanguis Challis transformation system. The chimeric plasmid containing the dextranase gene will be utilized to transform dextranase-negative mutants of S. mutans GS5 to the dextranase-positive phenotype in order to assess the role of this enzyme in sucrose-dependent colonization. In addition, the S. sanguis dextranase-positive clone will be utilized to determine whether these organisms present on model tooth systems will antagonize subsequent colonization by S. mutans.